Most Polaroids don't carry much of a used value these days; the film is expensive and hard to get, and the vast majority of the cameras were mediocre at best—something along the lines of Kodak's Brownies, or one step up. But SX-70s were a technological marvel at the time, and very expensive. They still carry a lot of residual value today. How much? Depends on the model and the condition, and so on. I think $50 is usually a good starting point.
I never cared much for Polaroids but always thought it would be interesting to have one. I was fortunate—a thrift shop had it collapsed and obviously didn't know what it was. I assume they thought it was probably a flask, as they had it in a bag hanging on a wall with silverware, kitchen utensils and such, priced at $5.99
The SX-70 made a huge splash when it was originally introduced.